The present invention is directed to control devices for bicycle transmissions and, more particularly, to an apparatus that uses rotational power from a rotating crank, axle or some other member to assist the operation of the bicycle transmission.
A typical bicycle transmission is operated by a shift operating wire connected between the transmission and a manually operated shift operating device mounted on the handlebar. The rider operates the shift operating device to selectively pull or release the shift operating wire which, in turn, operates the transmission in the desired manner.
One of the goals of bicycle transmission design is to make the transmission easy to operate with a minimum amount of effort. This involves minimizing the force needed to operate the shift operating device as well as minimizing the amount of unnecessary movement of the shift operating device. In the case of bicycle transmissions such as derailleurs which are used to shift a chain from one sprocket to another, the amount of force needed to derail the chain from one sprocket and move it to another can be quite large, especially when the destination sprocket is substantially larger than the originating sprocket and the rider is exerting substantial pedaling force on the chain. The necessary operating force can be reduced by operating the shift operating device when only a small pedaling force is being applied to the chain, but that requires the rider to consciously alter his or her pedaling technique and/or consciously operate the shift operating device only when a small pedaling force is being applied to the chain. That can be very distracting, especially in a racing environment. Also, the actuation ratio of some derailleurs may be somewhat large. Consequently, the shift operating wire must move a substantial distance to fully move the chain from one sprocket to another, thus requiring the rider to move the shift operating device by a correspondingly large amount.
The present invention is directed to an assist device for shifting a bicycle transmission wherein very little force is needed to operate the transmission, the shift operating wire needs to be pulled or released only by a very small amount, and the assist device automatically determines when to perform the shifting operation. In one embodiment of the present invention, an assisting apparatus that uses power from a rotating member to assist the operation of a bicycle transmission includes a mounting member; a cam member coupled to the mounting member for rotation around a cam axis, wherein the cam member has a cam surface; a cam follower cooperating with the cam surface for moving in response to rotation of the cam member; a transmission actuating element coupling member for communicating movement of the cam follower to a transmission actuating element; a first coupling member coupled for rotation of the cam member, wherein the first coupling member moves between a first engaged position and a first disengaged position; an operating member for moving the first coupling member to the first engaged position; and a decoupling member that moves the |first coupling member to the first disengaged position in response to a rotational position of the cam member. The first coupling member selectively engages and disengages the rotating member so that the rotational force of the rotating member may be used to assist the shifting operation.
In a more specific embodiment, the cam follower comprises a cam follower lever having a first end that cooperates with the cam surface and a second end. The transmission actuating element coupling member, which may be a cable connector, may be coupled to the cam follower lever. The operating member, which may take the form of an operating lever, may include a hook or ledge for supporting the first coupling member in the first disengaged position. In such embodiments, the first coupling member moves radially inwardly relative to the cam axis to move to the first engaged position and thereby engage the rotating member, and the first coupling member moves radially outwardly relative to the cam axis to move to the first disengaged position and thereby disengage from the rotating member. The first coupling member rotates together with the cam member when the first coupling member engages the rotating member.
In such an embodiment of the present invention directed to a two-speed assist device, a second coupling member is coupled for rotation of the cam member, wherein the second coupling member moves between a second engaged position for engaging the rotating member and a second disengaged position for disengaging from the rotating member. The second coupling member is spaced apart from the first coupling member, and the first coupling member and the second coupling member are both coupled for rotation together with the cam member. The operating member, which again may take the form of an operating lever, includes a first control surface that supports the first coupling member in the first disengaged position when the cam member is in an initial position. In this case the mounting member includes a second control surface that supports the second coupling member in the second disengaged position when the cam member is in the initial position. After the cam member rotates together with the first and second coupling members by a prescribed amount, first disengaged position. A control surface on the operating lever returns the second coupling member to the second disengaged position. Thus, in this embodiment the cam member has two stationary steady-state positions. The cam surface may be configured such that the cam follower moves the transmission actuating wire to two different transmission operating positions.